Many highly productive oil and gas fields are found in unconsolidated or poorly consolidated rock formations, that is, rock formations in which the individual grains of sand making up the rock formation have not yet become cemented together by the passage of time. Wells in these formations are normally “cased” by lining them with steel pipe. The casing is “perforated” by detonation of an explosive charge or the like within the pipe so as to form orifices in the casing at the depths where it is anticipated that oil and gas will be usefully recovered.
One of the problems encountered in obtaining oil or gas from a subsurface earth formation is unconsolidated sand, which can be carried into the well bore along with the oil or gas. This causes damage to equipment and also necessitates that the sand be removed from the oil or gas which is produced. Furthermore, excessive sand production can cause the entire formation to collapse, necessitating that the well be cleaned out and, in many cases, that it be packed with “gravel,” a relatively coarser sand which then acts as a kind of filter. However, such methods are complex and expensive to perform. The problem can be alleviated by treating the formation sand with various chemicals to consolidate the sand particles. Before actual consolidation treatment is begun, a sample of the unconsolidated sand is tested for fluid permeability and other characteristics. The sample is then treated with the appropriate chemicals under simulated formation conditions. As new fluids and methods are developed, a test to effectively and efficiently determine the performance of the fluids and methods is required.
One prior procedure for the simulated test involves placing a container, such as a metal cylinder which is closed at one end, on a vibrating table. With the table vibrating, a volume of water, approximately 35% of the cylinder capacity, is placed in the cylinder, and the unconsolidated sand is sifted into the cylinder until it is full of moist, compacted sand. The open end of the cylinder is then capped and the sample is checked for fluid permeability, using a light oil at residual water saturation. The sand sample is then treated to consolidate the particles and the permeability of the sample to diesel oil is determined. However, this method has the drawback that the sand sample often includes clay, silt, or other non-sand fractions that segregate within the sample during the test, making it difficult to obtain an accurate flow profile of fluid through the sample. Further, the vibration technique used is often not reproducible among sand samples having different fractions of clay, silt and other non-sand components.
Another prior simulation technique involves placing an unconsolidated sand sample in a vessel and compacting the sample between two pistons. Fluids are passed through the compacted sample to determine flow permeability before and after a consolidating fluid is added to the sample.
One prior art test includes placing unconsolidated sands in a tube with a filter cake on one exposed surface of the sand. Fluid is pumped through the tube in each direction to measure the effectiveness of the filter cake and fluid. However, this prior art method does not effectively simulate the fluid flow as it would be found in the wellbore during drilling.
Another prior art method includes drilling through an artificially-created sand bed. While this method effectively simulates the drilling process, it is costly and requires a lot of equipment and space to perform.
It would be an improvement to the art to have a test apparatus and method that effectively simulates the drilling environment while not requiring the space and equipment of prior art testing methods.